Recommendations for adding to tank

[vaughnkennedy]

I moved the shell to the top of one of my rocks and it looks more like it has short tendrils than cilia. I can't get a good enough photo with my camera. I looked at images of peanut worms and none of them look like what I have. I really just wanna know if it's harmful or not.

 

[Bifferwine]

More likely than not, it's harmless.